Altimeter or the like



Oct. 26 1943. M. N. FAlRB ANK ALTIMETER OR THE LIKE Filed Sept. 13, 19402 Sheets-Sheetyl Oct. 26, 1943. M. N. FAIRBANK 2,332,565

' ALTIMETER OR THE LIKE Filed Sept. 15, 1940 2 Sheets-Sheet 2 PatentedOct. 26, 1943 UNITED STATES: PATENT OFFICE ALTIMETEB OR THE LIKE MurryN. Fairbank, Weston, Mass.

Application September 13, 1940, Serial No. 356,619

Claim.

This invention relates to a new and improved altimeter, and moreparticularly to a device of the character described which is adapted tobe used on airplanes.

An object of the invention is to provide a device of the characterdescribed which may be readily and cheaply manufactured, and which isdurable and accurate in operation Other objects of the invention are toprovide, I

in a device of the character described, readily assembled and easilyoperated means for effecting an air-tight seal between the portions ofthe casings of the device; to provide a device of the characterdescribed in which operative elements may be readily mounted within thecasing; to provide, in a device of the character described, novel easilyassembled means for providing accurate gauge readings throughout theentire gauge scale; to provide manually adjustable means forcompensating for alterations in barometric pressure at the point oftake-off; and to provide novel operative means, including novel pressuresensitive means, for effecting alterations in the gauge readings.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the features of construction,combination of elements and arrangement of parts which will beexemplifled in the article hereinafter set forth and the scope of theapplication of which. will be indicated in the claims For a fullerunderstanding of the nature and objects of the invention, referenceshould be had to the accompanying drawings, in which:

Figure l is a front view in elevation, with certain elements shown indotted lines, of a device embodying the invention;

Fig 2 is a side view in section, and drawn to an enlarged scale, of thedevice shown in Fig 1 along the line 2-2;

Fig. 3 is a view in section of a portion of the device shown in Fig. 2and taken along the line .3-3;

Fig. 4 is a view in horizontal section of the device shown in Fig. lsomewhat enlarged and taken along theline l-; and

Fig. 5 is an enlarged fragmentary view of a portion of the device shownin Figs 2 and 4.

In the form of the invention shown in the portion ll of the casing. Theforward part of the casing is preferably provided with rearwardlyextending supporting elements, hereinafter described, upon which theoperative elements of the device are mounted. These elements and theforward part of the casing are preferably so designed that the operativeelements of the device may be easily assembled. When assembled, they areenclosed within the relatively light rear portion M of the casing, whichis adapted to seat against a rearwardly extending shoulder of theportion i2 of the casing, as'at it. I

An air-tight seal is efiected at the joint between the two portions ofthe casing by the provision of a supplemental ring member 08 positionedwithin the portion l4 and adapted-to bear against the resilient gasket20, which may be preferably of rubber. After the section it of thecasing has been slid into place, the ring member 68 is drawn forwardlyagainst the gasket 20 by means of the screw elements 22 which extendthrough the dial face 26, as shown for example in Fig. 1. These screwsare threaded into the ring element 88, as shown in Figs. 2 and 4, and,as they are tightened, the ring element i8 is drawn towards the frontportion M of the casing, thus forcing the resilient member 20 againstthe rear portion of the casing, and causing the seal between the twoportions of the casing to become air-tight Such a seal is preferred, forwhile it is intended that the device-shall respond to alterations inbarometric pressure occasioned by alterations in altitude of theairplane equipped with the device, it is desirable that the device beshielded from alterations in the pressure of the atmosphere within theplane itself, as atmospheric pressure within the plane may fluctuateindependently of external atmospheric pressure Accordingly means areprovided, for example the pipe 38 leading directly from within thecasing of the device to a static tube outside the airplane in which thedevice is mounted With such an arrangement the device will respond onlyto alterations in external atmospheric pressure .Means are provided, forexample the drilled lugs 24, preferably associated with the frontportion l2 of the casing, for affixing the device to a suitableinstrument panel, not-shown.

Within the casing and at the forward part thereof there is provided adial face 26 hearing suitable evenly-spaced indicia 28 indicative of thealtitude reached by the plane equipped with the device. The dial 26 maybe mounted upon screws 82. A glass cover-plate 84 is provided which isheld in place by a snap ring 88 which forces the glass plate asainst thegasket 40.

A small window 42, shown clearly in Fig. l, is

provided in the gauge face 28, and, in registrywith this window, thereis provided a walking beam 44 bearing on its forward face a stripbearing a series of indicia 48, shown for example in Fig. 1. The deviceis so adjusted that with each complete rotation of the needle orindicating element 88 a new numeraLof the series of indicia 48 isbrought into position behind the window 42 in the dial face. This isaccomplished by the downward movement of the front of the walking beam44, as shown in Fig. 2, which in turn is caused by an expansion of thebellows 41 inresponse to a lowering of the outer atmospheric pressure,as will be hereinafter described.

The bellows 41, the walking beam 44, and the other operative elements ofthe device, are in large part mounted upon the rigid frame elementswhich are integral with or securely affixed to the heavier forward partof the casing. These elements, in the form of the invention shown,comprise a rearwardly extending cylindrical element 48 and a verticalelement It which, as-shown in Fig. 4, is preferably so shaped as toposition most of the operativ elements of the device to one side of theelement 48, which is not centrally disposed in the device.

Pivotaliy connected as at I! to the upper portion of the element 88there is a substantially horizontal arm 84, to the rear end of which thewalking beam 44 is pivotally connected. as at 86. At the lower end ofthe element 88 there is pivotally connected, as at 88, a substantiallyhorizontal forwardly extending arm 80, which is connected to the arm 84by means of the element 82, which is countersunk in the arm 88 and inthe adjustable screw 84. The spring 88, which-is amxed to the element54, as at 88, and to the element 80, as at ill, serves to hold these twoelements firmly against the vertical element 82, so that as the element8!! is pivoted about the pivot I8, its motion is translated to theelement 84, which pivots about the pivot 82.

It will be understood that the relative positions of the arms 84 and Ilmay be altered within reasonable limits by adjusting the screw 84. Thisalteration is ordinarily only necessary when the device is firstassembled to so adjust the element 84 with respect to the element 88that the device may function in the manner hereinafter to be explainedto giv an accurate reading.

The forward portion of the arm 80 is held downwardly against theball-bearings 12, or any other suitable element, by the spring 14,whichmay be affixed to the portion 21 of the frame means. Theball-bearings 12 rest upon the tapered end 18 of a manually adjustablethreaded element I8. As this element is moved to the right. as shown inFig. 2, the: ball-bearings 12 are raised in the channel in the frame inwhich they are positioned and they elevate the forward portion of thearm 80. This, in turn, causes the a transverse frame element 21 by meansof the eating needle 30. Thus, by adjusting the element I8 andhenceraising or lowering the forward portion of the arm 80 against theaction of the spring 14, the indicator 80 can be set at zero reading onthe dial, irrespective of changes in atmospheric pressure at th point oftake-off.

At the rearof the device and mounted upon the horizontallyextendingframe element 48 is the evacuated bellows 41 and its associatedelements. In the form of the invention shown in the drawings the base ofthe bellows rests upon a lateral extension 82 of the fram element 48, towhich the bellows is rigidly mounted, as at 84. The upper portion of thebellows supports a vertically extending arm 86 terminating in thepivoted connection Iii with the rear end of the walking beam 44, aspreviously described. Within the bellows there is provided a helicalspring 88 under compression, the spring acting constantly to force thebellow outward against atmospheric pressure which tends to compress theevacuated bellows. A preferred arrangement is one in which the bellowsstructure itself has been so treated as forward portion of the arm 54 torise and the to relieve initial strain in the metal thereof. Under thesecircumstances, the tendency of the bellows to expand with a reduction ofpressure within the casing is due almost solely to the spring 88 which,as has been pointed out. is under compression at atmospheric pressures,and tends to elongate as the pressure is reduced. With such anarrangement a much more accurate reading can be secured, as the devicecan be adjusted substantially to respond to the reaction of the springalone and thus the well known lag in the response of bellows memberssuch as that shown at 41 is reduced.

A preferred means for mounting thespring element is shown clearly inFigs. 2 and 3. The ends of the helical spring element are bent inwardlyas shown in Fig. 3 to provide upper and lower arms 80. These arms arecountersunk as at 82 along the axis of the helix formed by the spring,and pin means 94 are provided in the upper and lower portions of theframe holding 7 the bellows element. These pins sit in the countersunkportions 82 and thus hold the spring firmly and centrally in thebellows. The entire spring action is thus along the axis of the helixformed by the spring and,.with the structure as shown and described,there is no tendency for a portion, however small, of the spring to comeinto contact with any other portion thereof during the operation of thedevice. 86 illustrates the tube through which the bellows member isevacuated.

It will be apparent that with a device such as has been described a dropin atmospheric pressure within the casing ID will cause an expansion ofthe bellows element 41 by means of the out ward thrust of the springelement 88. This will raise the arm 86 and the pivot 80. thus elevatingthe rear portion of the walking beam 44, which pivots about the point 56so that the forward portion of the beam will be forced downwardly.

Means are provided to convert this downward movement of the forwardportion oi the walking beam into a rotation of the needle 30, so thatchanges in altitude may be read directly from the position of the needlewith respect to the dial face 26. The needle is mounted upon the end ofa spindle shown generally as at I00. A detailed drawing of the spindleand its associated elements is shown in Fig. 5. The forward portion ofthe spindle comprises a member I02 mounted in a bearing I04 of the frame21. The

2,832,505 needle 30 as shown is mounted upon the outward end 'of themember I02. The rear portion of the spindle shown as at I06 is mountedin an arm I08, which in turn is rigidly afllxed to the frame 21 by theposts I I (Fig. 4) in which it is mounted and which are riveted into theframe.

The main body of the spindle I00 comprises two portions,a taperedportion H2 at the forward end of the spindle, and a generallycylindrical portion H4 at the rearward end of the spindle. About thetapered portion H2 there is coiled a wire H6 which is aflixed to thetapered portion of the spindle and which provides an inclined groovebetween adjacent portions of the wire. As shown in Fig. 5, this grooveis adapted to receive a thin, pliable wire II 8 which may be amxed tothe upper portion of the walking beam element 44 as at I20 (Fig. 2).This Wire IIB may preferably be formed of a plurality, for examplethree, strands of tungsten wire of small diameter, for example theindividual strand may have a diameter of approximately .001 of an inch,and the three strands may be woven to form a cable. This wire ispreferably afilxed to the large end of the tapered portion H2 of thespindle I00 in the last groove formed by the coiled wire IIB, as forexample at I22, so that rotation of the spindle causes the wire H8 towind in the groove, each full rotation of the spindle winding the wireIIB once around the spindle and progressively in a group of shorterlength. It will be apparent that the first rotation of the spindle willcause a greaterlength of the wire H8 to be wound thereon than the secondrotation. As shown in Fig. 5, the device is adapted for four successiverotations of the spindle, each drawing a smaller amount of the wire H8on to the tapered portion I I2. Each rotation of the spindle causes onecomplete rotation of the needle 30 and corresponds to such downwardmovement of the walking beam 44 as causes the next successive numeral inthe.list of indicia 46 on the front thereof to come into position behindthe window 42 in the dial face 26. At the end of one complete revolutionof the spindle, for example, the walking beam 44 will have been loweredto such an extent that the numeral 4 appears in the window 42 and, atthe end of four complete revolutions of the spindle, the numeral I6 willappear in the window 42. This will be apparent from an inspection ofFig. 1. The de-. vice is thus adapted to record changes in elevationfrom zero to 16,000 feet.

The tapering of the spindle, as shown clearly in Fig. 5, resulting in aless downward movement of the walking beam 44 with each completerevolution of the spindle, is to compensate for the fact that at higheraltitudes the bellows 41 and its associated elements expand somewhatless with an increase in altitude of, for example, 1,000 feet than atlower altitudes and, since the dial is fixed, means are provided tocompensate for the decreasing expansion of the bellows element withchanges in barometric pressure at high altitudes.

While the wire H8 may be affixed as at I22 to the spindle, in thepreferred form of the invention an extension of the wire is coiledaround the cylindrical portion of the spindle H4, as for example at I24, and the end of the wire may be afilxed,'as at I26, to a springelement I28 affixed to the walking beam 44, as at I30. The spring I28holds the wire II8 under tension and, as the walking beam is lowered,its pulls down upon the lower end of the wire I I8, thus unwinding thecoils I24 from the cylindrical portion H4 oi the spindle, andthus inturn causing the spindle to rotate and to wind thereupon the wire H8 inthe manner previously described. It will, of course, be apparent thatthere should be suiilcient take-up wound upon the cylindrical portion H4of the spindle so that four complete turns of the spindle may be made.

It will be apparent that other means for causing a rotation of theneedle element 30 may be substituted for wire and spindle means shownand described. For example, a fine cable might be substituted for thewire H8 with the addition of a hair spring tending to rotate the spindleinstead of the spring I28. Other modifications in the structure will beobvious to those skilled in the art.

The operation of the device will be apparent from the description. Thedevice is first set at any desired position, as for example at zeroreading, by rotation of the element 18, which in turn causes anadjustment of the walking beam and of the needle element 30 through thepivoting of the arms 60 and 54 about the pivots 58 and 52 in the mannerpreviously described. After this initial adjustment, the device is readyfor operation. Changes in altitude result in changes in expansion orcontraction of the spring 08 within the evacuated bellows 41, aspreviously described, and these changes are translated to the walkingbeam 44 through the pivot 80. As the front part of the walking beam 44is lowered or raised it causes a rotation of the spindie I00 with acorresponding rotation in the needle 30. The spindle I00 is constructedto compensate for changes in the degree of expansion and contraction ofthe bellows element 41 with changes in altitude.

The element I32 shown in Figs. 2 and 4 is a counterbalancing weightaflixed to the walking beam 44 to aid in balancing the elements of thedevice.

Means are also preferably provided for adjusting the position of thepivot and the upper end of the bellows element 41 with respect to thewalking beam 44. An adjustment of the position of this pivot isdesirable in connection with the initial adjustment of the various partsof the device. As shown in the drawings, this is accomplished byproviding a slidable plate I40 in which the pivot is mounted, the plateI40 being held in position between extending flanges I42 from thewalking beam 44 by means of a screw I44 threaded in the plate I40 andextending through the slot I46 in the element 44. It will be apparentthat the position of the plate I40 may be controlled within the limitsof motion of the screw I 44 within the slot I46.

Since certain changes may be made in the above article and differentembodiments of the invention could be made without departing from thescope thereof, it is intended that all matter. contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent 1. In an altimeter, in combination with presmovethrough a greater distance at low pressures than at high pressures inresponse to the same extent of motion of said movable scale, said meanscomprising a tapered spindle upon which said pointer is mounted andacable mounted for motion with said movable scale and adapted to causerotation of said spindle, there being an aperture in said fixed scale,said movable scale bearing a series of indicia thereon and being sopositioned with respect to said aperture that successive ones of saidindicia are brought into view therethrough with each complete rotationof said pointer.

2. In a device of the character described, in combination, meansproviding a two-part casing, means for rendering substantially air-tightthe joint between said casing parts after said parts have beenassembled, frame means mounted within and extending from one of saidcasing parts, pressure sensitive means carried by said frame, ascale-carrying beam pivotally connected to said frame and movable inresponse to motion of said pressure sensitive means, cable means afflxedto and movable with said beam, a tapered spindle mounted in said frameand engaged by said cable, a second fixed positioned scale having anapcr-. ture therein, and a pointer mounted to rotate with rotation ofsaid spindle and positioned for rotation adjacent the face of saidfixedscale, said first-mentioned scale bearing a, eries 1 1ndicia so positionthereon that a succeeding one of said series is brought into viewthrough the aperture in said fixedly positioned scale with each completerotation of said pointer.

3. In an altimeter, in combination, pressure sensitive means comprisingan evacuated bellows having mounted therein, under compression, ahelical spring, the mounting means for said spring being positionedalong the axis of the helix formed by said spring, a dial having anaperture therein, a scale thereon, a movable pointer associatedtherewith, and means for mechanically connecting said pointer to saidbellows whereby motion of said pointer is responsive to expansion andcontraction of said bellows. said connecting means comprising a taperedspindle, cable means windable thereon and a pivotally mounted armaillxed to said cable means, said arm carrying, on the endtthereoi'adjacent said first-mentioned scale, a second scale, said second scalebearing a series of indicia so positioned thereon that a succeeding oneof said series is brought into view through the aperture in the dialwith each complete rotation of said pointer.

4. Pressure sensitive means for use in an altimeter or the like,comprising an evacuated metallic bellows and a helical spring mountedwithin said bellows under constant compression, the active length ofsaid spring remaining constant under all conditions of operation of saidpressure sensitive means, the means for mounting said spring within saidbellows being positioned along the axis of the helix formed by saidspring and comprising a pair of inwardly projecting pointed elements,each end of said spring being turned inward and being to engage one ofsaid pointed elements.

5. Pressure sensitive means for use in an altimeter or the like,comprising an evacuated metallic bellows and a helical spring mountedwith in said bellows under constant-compression, the active length ofsaid spring remaining constant under all conditions or operation of saidpressure sensitive means, the means for mounting said spring within saidbellows being positioned along the axis of the helix formed by saidspring and comprising a plurality of recess-providing ele ments and aplurality .0! pointed elements, one pointed element seated in each saidrecess, each end of said spring being turned inward and comprising oneelement of said mounting means.

MURRY N. FAIRBANK.

provided with a recess adapted CERTIF ICAIE OF C ORREC TI ON Patent No.2,552,565. October 26, 19145.

HURRY N. FAIRBANK- 'It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows: Page 14., first column, line 55,claim 2, for "fixed" read"fixedlyline same claim, for "position" read --pos itioned--; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of January, A. D. 191-411..

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

